Simple One-Pot Synthesis of Thieno[2,3-b]thiophene Derivatives under Solid–Liquid PTC Conditions. Useful Starting Material for the Synthesis of Biological Active Compounds

A variety of thieno[2,3-b]thiophenes were prepared under phase-transfer catalysis conditions. The reaction of diethyl 3,4-dimethylthieno[2,3-b]thiophene-2,5-dicarboxylate with hydrazine hydrate gave the corresponding hydrazide derivative which was also subjected to react with acetylacetone, ethyl acetoacetate, malononitrile, CS2, phenyl isothiocyanate, p-chlorobenzaldehyde and diazotization to afford the described compounds. Treatment of 2,5-bis(azidocarbonyl)-3,4-dimethylthieno[2,3-b]thiophene with ethyl cyanoacetate, diethyl malonate or malononitrile gave the corresponding triazole derivatives.